This invention relates to devices for inspecting the leads of integrated circuit or semiconductor devices. Known semiconductor device lead inspection systems are used to determine the position and orientation of semiconductor device leads after manufacture to find defects in the leads, such as bent leads, tweeze leads and the like. Prior art systems are mainly intended to provide a two dimensional view of the leads, which cannot be used to measure the lead standoff and coplanarity. In some cases, two or three imaging devices with various viewing angles are used to inspect device leads. In existing devices, the position of lead standoff may be measured from an optical reference such as a track upon which the semiconductor device is positioned for purposes of inspection. In this event, the accuracy of positioning the device on the inspection station can affect the accuracy of the measurements of the lead positions.
It is an object of the present invention to provide images of a semiconductor device and its leads which provides geometrical information of the lead positions with respect to the edge of the semiconductor device body.
According to the invention there is provided an apparatus for providing first and second backlit images of a semiconductor device edge and leads extending therefrom, the images being representative of first and second viewing angles corresponding to first and second different optical axes, as measured in a plane perpendicular to the device edge. At least one illuminator provides diffuse backlight illumination of said device edge and leads along the first and second optical axes. A triangular prism is arranged with a first optical surface facing the device edge and intersecting the first and second optical axes, a second optical surface forming an acute angle with the first optical axes, and a third optical surface. The first and second surfaces are at selected angles to the first and second optical axes to cause a first image of the device edge and leads along the first optical axis to be reflected by the second optical surface and emerge from the third optical surface in direction corresponding to a third optical axis, and to cause a second image of the device edge and the leads along the second optical axis to be reflected by the second optical surface and the first optical surface and emerge from the third optical surface in a direction corresponding to the third optical axis.
A camera is arranged to capture the first and second images along the third optical axis. In one arrangement the illuminator is an illuminated platform for holding the device. The camera may be arranged on a side of the device opposite the illuminated platform when the device is received on the platform. In one arrangement for providing backlit images of device edges and leads on two opposite sides of a semiconductor device, there are provided two triangular prisms on opposite sides of the device and on opposite sides of the third optical axis. In a preferred arrangement the first and second optical surfaces intersect at an angle of about 30 degrees. The prism may be a right angle prism, or an isosceles triangular prism, wherein the first and second optical surfaces form equal angles with the third optical surface. The third optical surface may be perpendicular to the third optical axis. The first and second optical paths preferably intersect the second optical surface at an angle that is greater than the critical angle, measured from the normal direction of the second optical surface, and the third optical axis preferably intersects the first optical surface at an angle that is greater than the critical angle, measured from the normal direction of said first optical surface.
According to the invention there is provided a method for forming first and second backlit images of a semiconductor device edge and leads extending therefrom, wherein the images represent first and second viewing angles corresponding to first and second optical axes as measured in a plane perpendicular to the device edge. The device edge and leads are illuminated with backlight diffuse illumination radiating in the directions of the first and second optical axes. A triangular prism is arranged having a first optical surface facing the device edge, a second optical surface forming an acute angle with the first optical surface and a third optical surface. A first image of the device edge and leads is reflected by the second optical surface in a direction emerging from the third optical surface corresponding to a third optical axis. A second image of the device edge and leads is reflected by the second and first optical surfaces in a direction emerging from the third optical surface corresponding to the third optical axes. The first and second images are captured along the third optical axis.
The illumination may be supplied by at least one illuminator arranged to radiate in the direction of the first and second optical axes toward the device edge and leads. The first and second backlit images may be captured on a single image plane of a camera on a side of the device opposite the illuminator. Two of the prisms may be provided on opposite sides of the device; whereby the first and second images of the edges and leads on opposite sides of a semiconductor device are reflected in directions corresponding to the third optical axis; and wherein the first and second images of each of the device edges and leads are captured.
For a better understanding of the present invention, together with other and further objects, reference is made to the following description, taken in conjunction with the accompanying drawings, and its scope will be pointed out in the appended claims.